This invention relates to a solid-state image sensing device, and more particularly to a structure suitable for miniaturized and many pixel implementation in a device.
As an example of CCD area sensors capable of providing high resolution of solid-state image sensing devices using charge transfer devices, it is known to have an area sensor of a structure in which photosensitive elements producing signal charges of two pixels constituting one line are arranged adjacently to each other in a column direction (vertical direction). However, in CCD area sensors generally used as a sensor for civil use, with a view to reducing the number of transfer stages requiring a broad area because of miniaturization requirement, a readout system is employed to add signal charges of two pixels adjacent in a column direction to read them out.
FIG. 1 is a plan view showing the configuration of a conventional solid-state image sensing device. Photosensitive element trains 11, 12, ... 18 each comprised of six photosensitive elements 1 to 6 are provided, and column transfer sections 21, 22, 23, 24, 25, 26, 27 and 28 each comprised of three transfer stages 7, 8 and 9 are provided adjacently to these photosensitive element trains. The transfer stage 7 corresponds to the photosensitive elements 5 and 6, the transfer stage 8 corresponds to the photosensitive elements 3 and 4, and the transfer stage 9 corresponds to the photosensitive elements 1 and 2.
Furthermore, S11, S21, ... S61 represent signal charges stored in the first photosensitive element train 11, and S12, S22 ... S62 represent signal charges stored in the second photosensitive element train 12. Reference symbols are similarly attached to other succeeding signal charges. For example, S18, S28, ... S68 represent signal charges stored in the eighth photosensitive element column 18.
At the lower part of FIG. 1 of the photosensitive element trains and column direction transfer sections, a row direction transfer section 10 for carrying out a transfer in a row direction (in a direction from the right-hand side to the left-hand side of paper) is provided. This row direction transfer section 10 includes transfer stages 31 to 38. An output circuit 39 is connected to a final transfer stage 31 of the row direction transfer section 10. This output circuit 39 reads out signal charges to the external.
In this solid-state image sensing device, a first field signal is formed by adding and transferring signal charges of two photosensitive elements adjacent in a column direction (in upper and lower directions of paper) to read them out to the external, and a second field signal is formed by adding and transferring signal charges of two photosensitive elements adjacent in the column direction and combined in a manner different from the above to output them. Further, by interlace-synthesizing two field signals, one frame signal is provided. Such a mode is called a field storage mode.
The operation of the above-mentioned conventional solid-state image sensing device will now be described by drawing attention only to one field.
Signal charges S11, S12 ... S18 of the first row and signal charges S21, S22 ... S28 of the second row, signal charges S31, S32 ... S38 of the third row and signal charges S41, S42 ... S48 of the fourth row, and signal charges S51, S52 ... S58 of the fifth row and signal charges S61, S62 ... S68 of the sixth row are transported to corresponding transfer stages, and are added thereat, respectively. Subsequently, signal charges S11+S21, S12+S22, ... S18+S28 correspondingly belonging to the first row of the signal charges added in a manner stated above are subjected to parallel-transfer to corresponding transfer stages 31 to 38 of the row direction charge transferring section 10. By transfer in a row direction of the row direction charge transfer section 10, signal charges are sequentially transferred to the output circuit 39, and are outputted therefrom to the external.
Then, added signal charges S31+S41, S32+S42, ... S38+S48 of the second row and those S51+S61, ... S58+S68 of the third row are outputted by the operation similar to the above. In this way, all signal charges can be outputted.
Meanwhile, in such a charge transfer device, since transfer stages 31 to 38 of the row direction transfer section are formed in such a manner that they are connected to respective transfer sections 21 to 28, the dimension in a row direction of one transfer stage must be formed so that it is equal to the arrangement pitch in the row direction of the photosensitive elements.
Furthermore, since four-phase drive is generally carried out in the row direction transfer section, one transfer stage is comprised of four electrodes. For this reason, the dimension of one electrode is one fourth or less of the pixel pitch. Accordingly, when the pixel pitch is reduced for the purpose of realizing miniaturization or many pixel implementation, high level miniaturization technology is required for forming the row direction transfer section.
On the other hand, if the number of photosensitive elements in a row direction is increased, the transfer rate required for reading out charges of one row within a predetermined time interval in conformity of the television system becomes high. Namely, the row direction transfer section must operate at a high frequency in proportion to the number of photosensitive element trains. This results in the problem that the burden on the transfer pulse supply driver is increased, leading to an increased power consumption.